Just do it mate ! Ive owned the 748 and 916 and both have there own advantages. Go for an early bike with the original graphics which are absolutely timeless IMO. As you run the 916 monster in your monster, i'd probably go for a 748 for the contrast so you really do have two different riding experiences.
Just be careful what you buy - with prices as they are there on early bikes there are unfortunatley many examples which have been owned by people who just dont know how (or cant afford) to look after them properly ! (my 748 track bike had 20k on the clock and hadnt been serviced for nearly 3 years !!!) Let me know if you need any help.
Finally - insurance, there are some good dual bike policies around which dont cost that much more than a single bike ones (ive just renewed my 888/S4R policy with protected no claims/breakdown etc for £260!)
A family run broker ive used for years - Laxtons (they alweays come up trumps!) - call Steve and tell him nathan bennett referred you...there number - 08704446365/3